In view of the rapid rise in world population and the concomitant increase in the need for food and raw materials, increasing the yield of useful plants as well as the increased extraction of plant storage substances, and in particular advances in the field of nutrition and medicine, are among the most urgent tasks of biological research. In this connection, the following essential aspects may be mentioned by way of example: strengthening the resistance of useful plants to unfavourable soil or climatic conditions as well as to disease and pests; increasing resistance to plant protective agents such as insecticides, herbicides, fungicides and bactericides; and a useful change in the nutrient content or of the harvest yield of plants. Such desirable effects could be produced generally by induction or increased formation of protective substances, valuable proteins or toxins. A corresponding influence on the hereditary material of plants can be brought about, for example, by inserting a specific foreign gene into plant cells without utilising conventional breeding methods.
The transfer of novel DNA sequences into plant cells using genetically manipulated plant infecting bacteria has been described in the literature in a number of publications, for example Nature, Vol. 303, 209-213 (1983); Nature, Vol. 304, 184-187 (1983); Scientific American 248(6), 50-59 (1983); EMBO-Journal 2(6), 987-995 (1983); Science 222, 476-482 (1983); Science 223, 247-248 (1984); or Proc. Natl. Acad. Sci. USA 80, 4803-4807 (1983). In these publications, the natural properties of these bacteria for infecting plants were utilised to insert new genetic material into plant cells. So far such insertion has been made using preferably Agrobacterium tumefaciens itself or the Ti plasmid thereof, and also cauliflower mosaic virus.